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LanguageCert Practice Reading: Part 3: Multi-Text Attribution ID: #60291 Easy Cloud Seeding and Weather Research
Instructions ›
Read the four texts below about cloud seeding, a weather modification technique that improves a cloud's ability to produce rain or snow. There are seven questions about the texts. Which text gives you the answer to each question? Choose the correct text (A-D) for each question. below about Cloud Seeding.
A Cloud seeding techniques that aim to artificially induce rainfall or snowfall only work if the clouds already have sufficient moisture and are accompanied by the right temperature and wind conditions. Any increases in precipitation are likely to be small, however, and it’s not always possible to tell whether any rain or snow fell naturally or whether it was triggered by seeding. There are two basic approaches to cloud seeding. One is to seed supercool clouds with silver iodide or ‘dry ice’. This causes ice crystals to grow which consume moisture from the cloud and then fall as snow or rain. The dry ice might be shot into the clouds via rockets or sprayed from a plane or a mountaintop. The second approach involves warm clouds and hydroscopic substances, like salt particles. These particles take on water vapor, and therefore become larger so that they fall faster. People have raised a few concerns about possible negative effects of cloud seeding, but any effects appear to be minor. Ionic silver is a toxic heavy metal, but the amount of silver iodide in seeded snow on the ground in mountainous areas is so small that extremely sensitive instrumentation is needed in order to detect its presence.
B Cloud seeding has been used to mitigate damage caused by hailstorms for years, and also to try to enhance rainfall and snowfall for water storage in reservoirs and underground. These localised projects are not to be confused with geo-engineering schemes which propose tinkering with Earth’s weather by modifying the planet’s ability to reflect solar energy. Currently, more than 50 countries worldwide participate in cloud-seeding operations. So, it seems odd then that the technique hasn’t actually been proven to work. Various studies have claimed annual precipitation increases of 10% or more. However, all these studies lacked statistical rigor. Some cloud-seeding critics raise concerns about interfering with nature. The amount of moisture in the atmosphere is determined by the balance between evaporation and precipitation. If cloud seeding is done on a large scale, it might lead to increased evaporation from locations outside the seeding area.
C In the 1940s, the atmospheric scientist Bernard Vonnegut found that particles of silver iodide can cause supercool clouds of water vapor to freeze into snow in the lab. Particles like silver iodide can provide a scaffold onto which water molecules can align themselves into a crystalline structure or, in other words, freeze. The technique has been used by governments on and off ever since. But despite decades of these cloud seeding operations, proof that the technique works outside miniature clouds created in the lab has been elusive. One explanation is that the instruments of past decades couldn't measure water droplet size in clouds in real time. Without knowing how a cloud evolves after seeding, scientists were unsure whether the silver iodide was having any effect. Another explanation is that the chaotic nature of weather makes controlled, natural experiments almost impossible. Once a cloud is seeded, it’s contaminated, and the experiment can’t be repeated because the same atmospheric conditions won’t reappear.
D Today, many entities – including government agencies, utility companies and ski resorts – seed clouds in an effort to boost winter snowfall in the mountains. More snowpack means more spring and summer runoff, which feeds local water supplies, irrigates crops and fuels dams that generate hydroelectric power. Cloud seeding has also been used in efforts to disperse fog at airports, boost summer rainfall and reduce hail. In fact, cloud seeding occurs in more than 50 countries worldwide. Yet despite all this activity, we still don’t know whether it works. We are atmospheric scientists, and we recently conducted a field study to evaluate cloud seeding as a means of enhancing mountain snowfall from winter storms. Our results clearly demonstrate that, at least under certain conditions, it’s possible to change the evolution and growth of cloud particles, leading to snowfall which otherwise wouldn’t have occurred. The next question is whether cloud seeding can be an effective tool for water managers in dry regions.
In which text does the writer mention that cloud seeding can also be used to reduce the incidence of certain weather features?
In which text does the writer imply that increased precipitation from cloud seeding might mean less precipitation elsewhere?
In which text does the writer say that the levels of harmful chemicals found in surface precipitation after seeding are insignificant?
In which text does the writer specify ways in which seeding materials actually reach the clouds?
In which text does the writer say that it is very difficult to prove the efficacy of cloud seeding in real-world conditions?
In which text does the writer suggest that the ability to cause precipitation at key periods can have many beneficial effects later on?
In which text does the writer suggest that cloud seeding is a low-level attempt at weather manipulation when compared with other methods?
AI explanationShows the answer. Tap to open.

Question Focus: Asks which text says seeding can cut down certain weather events.

Why this is correct: Text D says seeding can also reduce unwanted weather, like clearing fog and cutting hail. That matches lowering the number of certain weather features.

Question Focus: Asks which text hints that rain gained in one place is lost in another.

Why this is correct: Text B suggests a trade-off: large-scale seeding could dry out nearby areas through extra evaporation. That hints rain in one place means less in another.

Question Focus: Asks which text says the harmful chemicals left after seeding are tiny.

Why this is correct: Text A says the leftover chemical is so tiny that special tools are needed just to find it. That means the harmful amount is insignificant, as the question states.

Question Focus: Asks which text says how the seeding materials are put into the clouds.

Why this is correct: Text A lists the ways materials get up to the clouds - rockets, planes or a mountaintop. That directly answers how the seeding reaches the clouds.

Question Focus: Asks which text says proving seeding works outside the lab is very hard.

Why this is correct: Text C says real-world proof has been hard to get because weather is chaotic and each cloud can only be tested once. That is why it is difficult to prove it works.

Question Focus: Asks which text says making snow at the right time brings many later benefits.

Why this is correct: Text D shows many later benefits of winter snow: it feeds water supplies, waters crops and powers dams in spring and summer. That matches good effects that come later.

Question Focus: Asks which text says seeding is small next to bigger ways of changing weather.

Why this is correct: Text B contrasts small, local seeding with huge geo-engineering plans that change the whole planet. That shows seeding is a low-level attempt next to bigger methods.

General Tips:

  • Read all four texts first, since several share the same facts about cloud seeding.
  • Look for paraphrasing - the question rarely uses the text's exact words.
  • Watch for texts that sound alike; only one has the exact point the question needs.
  • For 'benefit' or 'problem' questions, find the text that clearly takes that side.

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